[Tony Parakka]

Ran the engine today and measured hot.. #4 was at 58/80.

The engine ran like it always has.. it did not seem any weaker than before.. So wondering if #4 has been weak all along..
I am in the Chicago area, and my static rpm at full throttle generally was 2150-2200.. (sensenich prop) Does this indicate a weak cylinder?

Plan is to remove the cylinder assembly and have it inspected and repaired.

My immediate question was could this have been prevented?
A number of friends at my airport suggest 100LL can cause this kind of failure (earlier we had determined the cylinder was leaking through the exhaust valve).. We did see balls of lead inside the plugs, and spatters inside the cylinder..
They also suggest switching to 91 octane gas
Others have recommended adding Marvel Mystery Oil at fillups to negate the effects of lead.

Switching to 91 octane makes a lot of sense.. Can it harm the airplane? Anyone on the forum burning 91 octane?
Thoughts on the Marvel mystery oil fuel additive?

thanks!

-tony

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